1. Field of the Invention
The present invention relates to a wireless communication system, and more particularly, a method of allocating frequency subbands in an ultrawideband (UWB) wireless communication system and an apparatus adopting the same.
2. Description of the Related Art
Much research has gone into finding methods utilizing a frequency band in an ultrawideband (UWB) wireless communication system with a very wide range of frequency bandwidth. Unlike wireless data transmission technology used in cellular mobile communication, satellite communication, and TV broadcasting in which a transmission data stream is carried on a reference frequency waveform called an RF carrier, in UWB technology, a data stream is transmitted by representing data of logic 0 and logic 1 by repeatedly generating a plurality of pulses with equal periods and a constant waveform without using a carrier, each pulse with a period shorter than 1 nanosecond.
That is, the UWB technology is a wireless communication technology in which a data stream is transmitted using a plurality of pulses playing a role similar to Morse code. For example, a data stream is transmitted by generating a plurality of pulses with a very short period (hundreds picoseconds) with a constant interval between each of the pulses and modulating the pulses by adjusting periods of the pulses with a short time (±Dt) before and after a predetermined time so that −Dt is used for transmitting logic 0 and +Dt is used for transmitting logic 1. Pluralities of data can be transmitted using the coded pulse signal.
FIG. 1 illustrates a network topology according to the IEEE 802.15.3 standard.
A network includes a plurality of devices 101 through 104 and a piconet coordinator (PNC) 105 which relays and manages data and commands among the devices 101 through 104. A piconet is a network including a plurality of devices and a PNC. The devices may be home appliances, such as TVs and camcoders, and any of the devices can be the PNC 105. However, in general, an audio/video (AV) receiver or a computer is the PNC 105. The PNC 105 receives a channel time request command from each of the devices 101 through 104 and allocates a channel time to each of the devices 101 through 104. Each of the devices 101 through 104 directly transmits data to other devices at the allocated channel time. The PNC 105 also performs power save mode management and authentication management. Through the authentication management, the PNC 105 distributes a key for protecting a payload, and each of the devices 101 through 104 transmits and receives encrypted data using the allocated timeslot and the distributed key. A multi-piconet is a network including a plurality of piconets.
FIG. 2 illustrates a distribution of a frequency band in a conventional UWB wireless communication system.
Referring to FIG. 2, a UWB frequency band allocated from 3.1 GHz to 10.6 GHz is divided into 16 subbands, each subband with a 520 MHz bandwidth. Bands 0 through 7 are defined as a low frequency group 210, a band 8 220 is a reserved band reserved for a new UWB communication system such as the ZIGBEE, and bands 9 through 15 are defined as a high frequency group 230. One of the subbands in the low frequency group 210 is not used in order to reduce interference in systems having a 5 GHz band allocated for a wireless LAN service as defined in the IEEE 802.11a standard. Therefore, the low frequency group 210 also has 7 usable frequency subbands.
FIG. 3 illustrates frequency hopping sequences used for the distribution of the frequency band of FIG. 2.
Referring to FIG. 3, 6 frequency hopping sequences suggested by a multi-user access method of a UWB wireless communication system that supports a multi-piconet in a wireless personal area network (WPAN) of the IEEE 802.15.3 standard are illustrated. A pulse is generated during a dwell time such that a 7-subband sequence is not duplicated among the 6 frequency hopping sequences, thus allowing 6 piconets to use the 6 frequency hopping sequences. Data is transmitted by generating a second pulse signal in a next subband of the frequency hopping sequences. The data to be transmitted is determined according to the generated pulse stream, wherein the pulse stream is generated by a UWB sender (not shown).
FIG. 4 illustrates another distribution of a frequency band in a conventional UWB wireless communication system.
Referring to FIG. 4, 15 frequency subbands with 520 MHz bandwidths are allocated for a UWB frequency band. Except one frequency subband corresponding to a 5 GHz wireless LAN frequency band defined in the IEEE 802.11a standard, 14 frequency subbands are used. The 14 frequency subbands are divided into a low frequency group and a high frequency group, each group having 7 frequency subbands.
FIG. 5 illustrates frequency hopping sequences used for the distribution of the frequency band in FIG. 4.
The sequences include 6 frequency hopping sequences. A pulse is generated during a dwell time such that a 7 subband sequence is not duplicated among the 6 frequency hopping sequences, thus allowing 6 piconets to use the 6 frequency hopping sequences. Data is transmitted by generating a second pulse signal in a next subband of the frequency hopping sequences.
In both of the embodiments, 6 frequency hopping sequences are designed so that frequency subbands are not duplicated. First frequency subbands of the 6 frequency hopping sequences are all the same because the first frequency subband is used as a reference frequency subband to easily search existing frequency hopping sequences when a new piconet is generated.
In a multi-user handling method in which one frequency hopping sequence is used simultaneously by a plurality of piconets in a multi-band UWB system suggested as a standard for a physical layer of a WPAN, even though the frequency hopping sequence is designed such that frequency subbands can be used flexibly according to a data transmission capacity of a single piconet by dividing the frequency subbands into a low frequency group and a high frequency group, the method cannot support more than 6 piconets. Furthermore, since subbands of the high frequency group are not used in a piconet in which a low data transmission rate is required, frequency usage efficiency is low.
Most multi-band UWB systems support a multi-piconet using frequency hopping sequences using the frequency hopping sequence algorithm described above. However, since the algorithm supports a maximum of 6 piconets at any given time and does not use subbands of a high frequency group in a piconet in which a low data transmission rate is required, a waste of frequencies occurs.